The present invention relates to an electrically controlled shutter mechanism for a photographic camera having a movable shutter element for opening or closing a light admitting aperture and a driving mechanism for moving the shutter element.
More specifically the invention relates to a shutter device for a photographic camera, especially for a medium or large format camera equipped for viewing with a focusing screen. The shutter is of the type having two shutter elements, each movable between a first and second rest position, for opening or closing the aperture and further having drive devices for the shutter elements which, for an exposure, are capable of moving the shutter elements sequentially with a set time interval in the same direction from the first to the second rest position.
An example of such a shutter device is the so-called focal plane shutter having rigid shutter elements, which, for the exposure of photographic materials, are capable of being sequentially moved with an arbitrary difference in time so that the leading shutter element opens the aperture for an exposure and the delayed shutter element then closes the aperture.
Several previously known designs of such shutter devices required relatively complicated mechanisms for controlling the drive devices for the shutter elements. Since the shutter elements must be returned to their initial position in a partially overlapping arrangement, following each shutter operation, so as to prevent an exposure during that process, the shutter elements also overlap in their initial position prior to the next shutter operation. For that reason the initial positions of the two shutter elements differ; and the difference in time between the start of the leading shutter element and the start of the delayed shutter element must deviate, when the shutter is activated, from the desired exposure time for that certain amount of time which transpires until the overlap of the shutter elements has been overcome. This reason, and others, inhibit the provision of a shutter device with exact, predetermined exposure times, especially when the aperture is relatively large, for example, when its diameter exceeds 50 mm, and when exposure times of 1/100th second or shorter are also required.